body {
    margin: 0;
    min-height: 100vh;
    font-family: Arial, sans-serif;
    position: relative;
}

/* 全屏背景层 */
.background {
    background-color: #000000;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -1;
    background-size: contain;/*cover*/
    background-position: center;
    background-repeat: no-repeat;
    opacity: 0;
    transition: opacity 1.5s ease-in-out;
}

.background.active {
    opacity: 1;
}

/* 内容层 */
.content {
    position: relative;
    z-index: 1;
    color: white;
    text-align: center;
    padding: 2rem;
    text-shadow: 1px 1px 3px rgba(0,0,0,0.8);
}
